Severe hypoxic hypoxia stimulates the sympathoadrenal system and causes hyperventilatory alkalosis. By adding to the energy deficit, the calorigenic action of both catecholamines and alkalosis may detract from the body's ability to survive when hypoxia decreases aerobic energy production. Conversely, catecholamine glycogenolysis may enhance survival by increasing glucose availability for anaerobic energy production. The potentially negative survival value of alkalotic and catecholamine calorigenesis and the degree to which increased anaerobic metabolism may affect survival will be examined in anesthetized, paralyzed, pump-ventilated dogs. The hypoxic end point will be the precipitous fall in blood pressure leading to death, the "circulatory crisis." Increase in arterial lactate and excess lactate are proportional to the estimated deficit in aerobic energy production by the hypoxic dog. These will serve as indices of time and intensity of the metabolic consequences of hypoxia whereas the more direct measure of oxygen uptake deficit will not if additional calorigenic processes begin after a control baseline is established. For similar amounts of oxygen deficits, therefore, the hypocapnic hypoxic dog will accumulate more excess lactate than the normocapnic hypoxic dog. If a beta-adrenergic blocking agent is used, the elimination of catecholamine calorigenesis should increase survivability of the hypoxic dog by the criteria of both time and net oxygen deficit for the same hypoxic stress in an untreated animal. To ascertain the survival value of increased anaerobiosis, the net oxygen deficits during severe hypoxia will be measured in beta- blocked normocapnic animals with and without supplementary glucose infusions. The net oxygen deficit more closely estimates the deficit in aerobic energy production when additional calorigenic processes associated with hypoxia are prevented by Beta-adrenergic blockade and by maintaining the animal normocapnic. Further, Beta-block prevents glycogenolysis so that glucose availability may become limiting to hypoxic survival.